1. Field of the Invention
The present invention relates to driving LED (Light-Emitting Diode) lighting fixtures and, more specifically, to controlling light intensity of LED lighting fixtures interfacing three-way sockets.
2. Description of the Related Arts
LEDs are being adopted in a wide variety of electronics applications, for example, architectural lighting, automotive head and tail lights, backlights for liquid crystal display devices, flashlights, etc. Compared to conventional lighting sources such as incandescent lamps and fluorescent lamps, LEDs have significant advantages, including high efficiency, good directionality, color stability, high reliability, long life time, small size, and environmental safety.
The use of LEDs in lighting applications is expected to expand, as they provide significant advantages over incandescent lamps (light bulbs) in power efficiency (lumens per watt) and spectral quality. Furthermore, LED lighting fixtures represent lower environmental impact compared to fluorescent lighting systems (fluorescent ballast combined with fluorescent lamp) that may cause mercury contamination as a result of fluorescent lamp disposal.
Conventional three-way incandescent bulbs contain two filaments, a low-power filament and a high-power filament. A three-way Edison socket controls output light intensity of the bulb using two AC voltage input lines. Specifically, a low-intensity setting is created by activating only the first input line, which is connected to the low-power filament of the incandescent bulb. For a medium-intensity setting, the three-way socket activates the second input line, which is coupled to the high-power filament. For a high-intensity setting, both input lines are activated.
However, when an LED lighting fixture is used in a three-way socket in place of a conventional incandescent bulb, multiple filaments are not available for providing different output light intensities. One solution to this compatibility problem uses two banks of LEDs, each connected to the output of a different single-channel LED controller or a different output of a multi-channel LED controller. The LED controller(s) take input voltage lines of the three-way socket and supply power to LED banks. However, the additional wire used to connect one of the LED banks to the second input line increases the manufacturing cost of the LED lighting fixture. Furthermore, illuminating different LED banks for different intensity settings causes uneven light distribution. Light may be redistributed using complex LED layouts or a diffusing lens, but these solutions add complexity and increase manufacturing costs for the LED lighting fixture.